Permanent magnet rotors are frequently used in dynamo electric machines such as motors and generators. Permanent magnets are secured to a rotor hub or shaft by any of a variety of means and care must be taken to assure that such securement prevents the magnets from moving either axially or radially. If axial movement is permitted, one or more magnets may not properly align with an armature, with the consequence that machine efficiency diminishes. If radial movement occurs, the probability of interfering contact between the rotor and the stator, and the resulting frictional drag and/or damage to machine parts, come into existence.
As may be expected, securement of magnets increasingly becomes a problem with increased rotor speeds due to the increasing forces tending to cause magnet movement, particularly in the radial direction, with the increasing centrifugal force accompanying increasing rotational speeds. Thus, in many instances where there are relatively high speeds, and permanent magnet rotors are required, securement of the magnets against both axial and radial displacement is accomplished by sandwiching the magnets between side plates which prevent axial displacement and by winding a fibrous material such as carbon fiber about the peripheries of the side plates and the magnets to provide radial retention. An example of this approach is found in U.S. Pat. No. 4,433,261 issued Feb. 21, 1984 to Nashiki et al. In addition to the foregoing general construction, Nashiki takes steps to prevent axial displacement of the wound fiber with relation to the side plates, and thus, the magnets. In particular, each of the side plates used by Nashiki et al is provided with peripheral, radially outwardly opening groove which also receives some of the fiber during the winding process. The fiber, after being wound on the rotor assembly, is secured with some sort of a setable resin and thus the fiber and resin combination become solidified within the peripheral grooves in the side plates. Because the resin impregnated fibrous body becomes solid, axial displacement of the fiber is obstensibly prevented.
However, this approach does not assure that fiber windings axially outwardly of the peripheral grooves in the side plates are positively retained against axial displacement. Loose fibers, not captured by the resin matrix, may exist at the ends of the fiber winding structure as a result of the application of insufficient resin in such locations. Even where sufficient resin is applied, the ends of the fiber windings define corners which, when the rotor is improperly handled, may become frayed, thereby loosening fibers from the fiber matrix.
If during operation of a machine in which the rotor is installed, the fibers become loose, they may impede proper operation of the machine by gumming up bearings or partially or wholly obstructing fluid flow paths. Furthermore, the discontinuities in the cylindrical surface of the rotor provided by such loose fibers contribute to windage losses.
Another difficulty encountered with rotors of the type disclosed by Nashiki et al reside in the difficulty in achieving a balance about the intended rotational axis of the rotor. When balance cannot be achieved, operation of the machine containing the rotor will result in the generation of vibration which can deleteriously affect the life of bearings and other machine components.
The present invention is directed to overcoming one or more of the above problems.